The present invention relates to a torque transmission apparatus for a vehicle having front-rear (two) driving axles, and in particular, to a front-rear axle driving torque transmission apparatus, which includes a differential gear means having a degree of freedom in setting a capacity of a clutch.
Various driving torque transmission systems for vehicles having front-rear driving axles have been already proposed, and have been practically used. Most of these systems uses a planetary differential gear so as to rotate a front axle and a rear axle at a different speed, and includes a clutch (lock operation is possible). The clutch is constructed in a manner of mutually coupling front-rear output shafts when a vehicle is running so as to prevent a differential rotation of the front-rear axles, and thereby, when one axle slips on and the other axle loses a driving force, transmitting a driving torque to the one which has no driving force.
Moreover, a dog clutch and a wet-type multiple disc clutch have been well known as the above clutch. In this case, the latter, that is, the wet-type multiple disc clutch has a structure in which the clutch is provided in an inner diametrical portion of an input gear on a first output shaft, as disclosed in Japanese Unexamined Patent Publication No. 50-147027, for example. The wet-type multiple disc clutch disclosed in Japanese Unexamined Patent Publication No. 50-147027 has the following merits. More specifically, a lock operation is possible during vehicle driving, and it is possible to reduce the number of components such as gears, bearings or the like, and thus, the structure can be simplified and made into a compact size as a whole.
However, in the case of the former, that is, the dog clutch, there is a problem such that no operation is made during vehicle driving. On the other hand, in the case of the latter, that is, the wet-type multiple disc clutch, there is a problem such that a degree of freedom is reduced because an installation space is limited in the case of changing a clutch capacity. More specifically, the clutch is situated in an input gear; for this reason, there is a problem such that it is difficult to readily make a modification for increasing a clutch capacity by increasing the number of clutch plates or enlarging a clutch disc diameter, for example.
The present invention has been made in view of the aforesaid problems in the prior art. It is, therefore, an object of the present invention to provide a front-rear axle driving torque transmission apparatus which is constructed in a manner that a front axle and a rear axle across between adjacent shafts, and an input gear, planetary differential gear means and a clutch are mounted as a unit in succession in an axial direction so as to improve a degree of freedom for setting.
In order to achieve the above object, the present invention provides a front-rear axle driving torque transmission apparatus, comprising: power input means; differential planetary gear driving means for rotating a front wheel side output shaft and a rear wheel side output shaft at a different rotational speed on the basis of a power inputted by the power input means; and clutch means for locking an operation of the differential planetary gear driving means so that the front wheel side output shaft and the rear wheel side output shaft can be rotated at the same rotational speed, the power input means, the differential planetary gear driving means and the clutch means being successively arranged as a unit in an axial direction in a state of crossing between the rear wheel side output shaft and the front wheel side output shaft arranged on the identical axial line.
According to the above construction of the present invention, the clutch means controls a lock state and a unlock state between the front and rear side output shafts, and further, the clutch means is arranged in an independent state on the side of the differential planetary gear driving means. Therefore, in the case of changing a capacity of the clutch means, a dimension of the clutch plate of the multiple disc clutch is freely changed, and also, the number of clutch plates is freely increased and decreased. Further, there is no limitation in the installation space, and thereby, it is possible to improve a degree of freedom with respect to a change. Furthermore, the clutch means is independently made into a unit, and thereby, it is possible to readily perform a maintenance for the clutch means.
In the present invention, preferably, the differential planetary gear driving means and the clutch means are arranged in a housing which crosses between the rear wheel side output shaft and the front wheel side output shaft arranged on the identical axial line, and is rotated around the axis integrally with the power input means. By this arrangement, the differential planetary gear driving means is made into a unit, and is firmly connected with the power input means, and thereby, it is possible to make compact a driving torque transmission apparatus.
Moreover, preferably, the housing rotating integrally with the power input means is composed of a housing integrally including a power input carrier of the differential planetary gear driving means, and a clutch housing of the clutch means. By this arrangement, the clutch means is independently made into a unit with respect to the differential planetary gear driving force, and thereby, it is possible to readily perform a maintenance for the clutch means.
In this case, preferably, the housing integrally including the power input carrier of the differential planetary gear driving means is a housing which is formed integrally with a carrier rotatably supporting a planetary gear around a coupled portion where the rear wheel side output shaft and the front wheel side output shaft are fitted, and the differential planetary gear driving means is included in the housing so that a ring gear connected with the rear wheel side output shaft by spline fitting and a sun gear connected with the front wheel side output shaft by spline fitting are engaged with the planetary gear. By this arrangement, each member of the differential planetary gear driving means is compactly received in the housing, and also, a load (weight) is ideally shared to each member.
Moreover, preferably, the clutch housing of the clutch means is provided with a hydraulic operating type ring-like disc clutch pack which locks the clutch housing, the front wheel side output shaft and the power input carrier so that they are coupled integrally. By this arrangement, it is easy to form an oil pressure circuit for operating a piston for pressing and releasing a clutch disc. Further, a clutch oil pressure is controlled, and thereby, it is possible to change a torque distribution by controlling an unlock state that the clutch oil pressure is zero and a lock state that the clutch is turned on by the oil pressure, and an intermediate oil pressure, and thus, to obtain a well functioned driving torque transmission apparatus.